Mass flowmeter



Aug. 24, 1965 c. F. ROBINSON MASS FLOWMETER Filed June 29, 1961 zz l INVENTOR. [#469155 F 1%5/Nf0/V ATTOP/VEK? pipe.

United States Patent MASS FLOWMETER Charles F. Robinson, Pasadena, Calif., assignor to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Filed June 29, 1961, Ser. No. 126,687 Claims. (Cl. 73- 194) This invention relates to an induction type flowmeter for measuring the mass flow rate of nonconducting media such as petroleum products.

. Inthe past induction type flowmeters have been provided for measuring the flow rate of conducting media. In general, these meters have included a pipe for transporting the conducting medium. and means for generating an alternating magnetic field across the diameter of the The conducting medium in passing through the magnetic field generates an which is perpendicular to'both the-direction of flow and the magnetic field. In particular, the magnitude of the induced is directly proportional to a product of the magnetic field flux density B and the velocity of the conducting medium v. To measure the induced and hence to provide an indication of the flow rate through the pipe, a pair of point contact type electrodes are set into the wall of the pipe perpendicular to the magnetic field. These electrodes are insulated from the pipe to prevent a short circuiting of the induced voltage. Since the voltage developed between the electrodes is proportional to the flow rate of the medium through the pipe, a detection of the magnitude of'the voltage induced between the electrodes represents a measure of the flow rate of the conducting medium through the pipe.

Although the above-described type of induction flowmeter has been extensively used to measure the flow rate of conducting media, its use has been limited thereto. In particular, it has been the teachings of the prior art, prior to this invention, that an induction-type flowmeter is only capable of measuring the flow rate of a medium if that medium were a conductor. In particular, it is commonly believed that induction-type flowmeters are limited to measuring the flow rate of a medium having a .conductivity of greater than mhos per meter.

Contrary to the teachings of the prior art, the present invention provides an induction type flowmeter for directly measuring mass flow rate of a nonconducting medium. To accomplish this, the present invention provides apparatus for measuring the induced voltage set up within a nonconducting medium due to the polarization thereof in passing through a magnetic field. In particular, in a basic form, the present invention includes a pair of parallel conducting plates disposed within the nonconducting mediumparallel to the direction of flow of the medium and an alternating magnetic field which is set up across the medium. Further, thepresent invention includes a capacitor shun-ting the parallel plates having a capacitance which is substantially larger than the capacitance of the parallel plates and a voltage detection device coupled across the shunting capacitor. The voltage which is developed across the pair of parallel plates when shunted by the large capacitor is directly proportional to the mass flow rate of the nonconducting medium passing therebetween. Accordingly, the voltage detected by the volt age detection device provides a direct indication of the mass flow rate of a nonconducting medium.

The above as well as other features of the present in.- vention may be more clearly understood by reference to the following detailed description when considered with the drawing, the single figure of which is a schematic representation of a basic form of the present invention.

As noted above, it is commonly known that when a ice conductor moves with a given velocity through a magnetic field, a voltage is induced within the conductor which is proportional to the flux density of the magnetic field and the velocity with which the conductor is moving. It is this principle which is applied in the prior art induction-type flowmeters for measuring the flow rate of conducting media. For various reasons, however, it has been taught in the prior art that similar principles of voltage induction could not be applied to measure the mass flow rate of nonconducting media. The present invention, however, contrary to these teachings, provides a fiowmeter utilizing induction techniques for measuring the mass flow of a nonconducting medium. In particular, the present invention in providing an induction-type fiowmeter for measuring the mass flow rate of a nonconductive medium utilizes the previously discovered fact that as -a dielectric (nonconducting material) moves in a magnetic field; the induced electric field acting on the elastically bound electrons of the dielectric displaces them relative to the nuclei and causes a resultant polarization (see pages 445-446 of Theoretical Physics, 1932 edition by Joos as translated by Ira M. Freeman, PhD. and published by Stechert & Co. of New York. More particularly, as pointed out in the cited reference, the

polarization charge 0' per unit area appearing at the opposite selected boundaries of the nonconducting medium moving through a magnetic field is given by the expression:

Substituting Equations 1 and 2 in Equation 3 gives:

K 1 v= K )vBd 4 In providing the above described condenser configuration, it is recognized that a certain amount of stray capacitance is present. Accordingly, the total capacitance C, of the configuration may be represented:

KA t m+ s where C represents the stray capacitance. This expression may be reduced to:

A r=m( +'Y) where From the above the expression (4), the voltage appearmg between the condenser plates due to the polarization of the nonconducting material then becomes:

(K 1)1)Bd fexpression:

which reduces to? (K1)vBd V (7+ 1) Q I As'is' commonly the density of a nonconducting alternating current signal from the, source 16 and operates to provide" at its output avoltage' signal which is in phase material and the dielectric constant K are related" by the Thus, substituting this expression for themass fiow rate into that for the induced voltage,ithe,expression for the induced'voltage becomes: 1 7

l rger);-

From expression jtll).ityappears that..the voltage developed between the, condenser plates. is directly propor-. In ac-' tional to. the ma-ssflo'wrate 3.wlclen;'y.is'large. cord'ance with the present, invention this is accompl shed with the alternating magnetic field, this voltage. signal being that due to the polarization charge carried at the condenser plates 12 and Y14,. Accordingly, the synchronousdetector. 26 rejects all other induced voltages which may be present in the system, Inp'articulargthe synchronous. detector. 26 rejects. an undesired. induced. voltage. "which is present all inductiontype flowmeters: This undesired indu'cedvoltage' is generallygcaused by .transformer effects of the alternating, magnetic field on the leads connecting the'condenserplates'12 and to the input ofthe alternating'current amplifier. Thisundesired induced voltage-signal isninety degrees' (907) out of phase with, the voltage signal due. to the polarization charge appearing at the condenser plates. 12 and'1'4t fiAcc-ording "ly, by synchronizing the detector 26 with the output of ".the source 16, the undesired induced voltage signal is reby shunting the condenser plates. with a large vcapacitor,

the rati-opf the total, capacitance to the. capacitance ,be-

tween the'plates thenrbeing large.

Although'with 7 large, the magnitudeiof the, voltage induced between the condenser plates is reduced, 'it' has been found in practice that voltages on the order of a few I a hundred microvoltsstill resultwhich signals are directly related to the. mass flo wrrate of the'nonconducting medium.. p i The above analysis may be; applied to the induction fiowmeter, fopmeasuring h m fl w i a said Pipe" having-f a componentof flux parallel .to the 0P- shown, theiinduction-type flowmeteriof ithe present inven 4 tioninclu desa pipe 10 insulatedwith nonconducting ma condtictingi rneditim, as'jrepresented in rthe. drawing} As terial. As represented, by;- Way. of example, the pipe '10 is' rectangular, having two of'its' opposite. inner faces composed, ,ofaconducting..mate1 ial- :to formi firstand second parallel conducting; plates 12- and314,:respectively;

Furthcr byt way of example onlygto, germrateranialter;

nating magnetic; field; through the, pipe- 10;; thePresenE. invention includes a source of alternating current signals I V an alternatin v ma t' w C represented at. 16, a horse shoe magnet 18, and a coil 20'; g gne'lc field through the medium per Accordingly, as'represented, current flowing from the source 16;;setsmpra;magneticlfieldwhiclr passes through the pipe 10 parallel to the-conducting plates 12 and 14.

. In the configuration;represented in the;draw ing,.a nonconducting medium flowing through the pipe 10 produces azpolarization, charge at-theplates' 12 and 14;- To detect a voltage between the condenser plates 12-and 14Which'; is proportionalrto .thema'ssaflow rateofthe nonconducting material, a capacitor 22. iscoupledacross the plates 12 and 14. In particular,- ill/accordance with the above' analysis, the magnitude ofi'the capacitance of the capacitor 22 is large relative to the capacitance of the plates 12 and a jected; onlythe desired inducedvoltage signal due to the .20

polarization-of the nonconducting -material being-measured by theyOltmeter'ZS. v I 5 *In view; of the above, it appears that by use of parallel plate conducting? electrodes shunted :by a large externalcapacitance, an induction fl'owmeter is provided for ac:

curatelymeasuring the mass flow rate of nonconducting media heretofore not-contemplated by theprior art.

' What isclaimed is: p Q

1'. Apparatus' for detectingthe mass flow rate of a medium having aconductivity of less than approximately 10*? mhos; per meter comprising: a pipe having a lining of nonconducting'material' for transporting the medium; first and sgcond' parallel plates of conducting. material disposed within said pipe parallel to the direction of flow of themedium; a capacitor coupled externally to said pipe across saidfirst' andsecond parallelplates, said capacitor having. a-ycapacita-nce which is substantially greater than the capacitance of said first and second =parallel plates; rneansrfor'generatingan alternating magneticfield through alternating magnetic field'for-detecting the voltage induced {between said-first and second parallel plates due to th flow of sa'idi mediumfthrough said magnetic field.-

2 ,Appara'tusifor detecting the ratetof mass'flow of anonconductinggmedium comprisingpmeans" for generating pendicular to :the direction ofrflow of the mediumyfirst and secondifplate's of n-onconductingmaterial mounted parallel to eachother', 'thermagnetic field, and the direction of flow of the medium; means for directing the flow 14.;- Accordingly, the. volta'gei developed between the condenser plates 12. and 14 whenithe capacitor 221s-v included is substantially proportional to the mass flow rate of the nonconducting materialflowing in'the pipe 10. As indicated above, this voltage is generally inthe ly,,to detect this voltage'withthe ordinary/alternating current voltmeter, it is'ne'c'es'sary first to. amplifythe voltage signal. T o'accomplish this analternating current amplifier 24 isconnectedacrossthe capacitor 22; i

As illustrated in the drawingthe o "tputof thcjalternating current amplifier 24{-'is coupled"'to a" synchronous detector 26, the output pr; whichis coupled to a voltmeter 28. The synchronou'srdetector 26 also'receive's the of the;medium betWeenEFthe pIates; a capacitor. shunting "said first :and" second ,pIates, said capacitor having a capacitance, which is la'rge"relative.to the capacitance of said first. and -second platesjand voltage detection means coupled across. saidcapacitor; 1

i 1 a .3; Apparatus; for detecting the mass flow rate ofa dielectric medium comprising? a pipe ,ha'virig'a lining of nonconductingmaterial for transporting the dielectric frnedium'rqfirst. and second parallel. conductive'plates disposed withm saidpipe parallel to the direction of flow of the medium; means for generating a'magnetic field extend- --ing. transversely'to saidpipe 'andparallel to said first and second plates; a' capacitor;shunting-saidfirst-and second a a q 7 plates, said capacitor'beinglarge relative tothecapacitance ofsaid first-and second 'parallel platesrandlmeans coupled across :sa'idcapacitor fgr. detecting'the' voltage induced between-said first and-second plates duetothe flow ofsaid dielectric mediumthrough said magnetic fieldf ertApparatus f or 'detecting' the mass flow. rate of a .dielectricj'rnedium comprising; a rectangular pipe having a two v opposite innerfa'ces composed. of a conducting material" for transporting? the "dielectric medium; means for generating an alternating magnetic field through said pipe transverse to said medium and parallel to said sides of conducting material; and means for detecting the voltage difference between the opposite sides of said pipe including a capacitor coupled between said opposite sides of said pipe and an alternating current voltage detection device shunting said capacitor, said capacitor having a capacitance greater than the capacitance of said opposite inner faces of said pipe.

5. In a flowmeter for detecting the mass flow rate of a fluid dielectric medium moving along a defined path and which includes first and second parallel plates of conducting material disposed Within and parallel to the direction of flow of the medium and means for generating an alternating magnetic field transverse to the direction of flow of the medium and parallel to said first and second plates, the combination of: a capacitor shunting said first and second plates, said capacitor having a capacitance which is substantially larger than the capacitance of said first and second plates and means shunting said capacitor for detecting the voltage induced between said first and second plates which is in phase with the alternating magnetic field.

References Cited by the Examiner UNITED STATES PATENTS 2,733,604 2/56 Coulter 73-194 RICHARD C. QUEISSER, Primary Examiner. 

1. APPARATUS FOR DETECTING THE MASS FLOW RATE OF A MEDIUM HAVING A CONDUCTIVITY OF LESS THAN APPROXIMATELY 10-7 MHOS PER METER COMPRISING: A PIPE HAVING A LINING OF NONCONDUCTING MATERIAL FO RTRANSPORTING THE MEDIUM; FIRST AND SECOND PARALLEL PLATES OF CONDUCTING MATERIAL DISPOSED WITHIN SAIDD PIPE PARALLEL TO THE DIRECTION OF FLOW OF THE MEDIUM; A CAPACITOR COUPLED EXTERNALLY TO SAID PIPE ACROSS SAID FIRST AND SECOND PARALLEL PLATES, SAID CAPACITOR HAVING A CAPACITANCE WHICH IS SUBSTANTIALLY GREATER THAN THE CAPACITANCE OF SAID FIRST AND SECOND PARALLEL PLATES MEANS FOR GENERATING AN ALTERNATING MAGNETIC FIELD THROUGH SAID PIPE HAVING A COMPONENT OF FLUX PARALLEL TO THE OPPOSING SURFACES OF SAID FIRST AND SECOND PARALLEL PLATES AND PERPENDICULAR TO THE DIRECTION OF FLOW OF SAID MEDIUM; AND PHASE SYNCHRONOUS VOLTAGE DETECTING MEANS COUPLED ACROSS SAID CAPACITOR AND TO THE MEANS FOR GENERATING THE ALTERNATING MAGNETIC FIELD FOR DETECTING THE VOLTAGE INDUCED BETWEEN SAIUD FIRST AND SECOND PARALLEL PLATES DUE TO THE FLOW OF SAID MEDIUM THROUGH SAID MAGANETIC FIELD. 